Then go for it, but just replace what needs replacing with 7 speed stuff. If you can't find NOS stuff on ebay, often if you post what you are looking for in some of the more techie bike forums, someone will have something sitting in a spare parts box they will either sell real cheap, or send you for shipping costs.
Maybe you could use this bike to learn more about maintenance, since yes, the bike shops will be less inclined to help you with parts that are out of production, but most of what you'll need to do isn't that hard at all.

